Olefin(-based) polymers, which include ethylene polymers, ethylene/.alpha.-olefin copolymers, ethylene/styrene copolymers, ethylene/cyclic clef in copolymers, propylene polymers and propylene/.alpha.-olefin copolymers, are used in various fields because of their excellent rigidity, mechanical strength, chemical resistance, moldability and heat resistance.
As catalysts used to produce these clef in polymers there are known titanium-based catalysts comprising solid titanium catalyst components and organoaluminum compounds, vanadium-based catalysts comprising soluble vanadium compounds and organoaluminum compounds, metallocene-based catalysts comprising metallocene compounds of transitional metals selected from Group 4 of the Periodic Table and organoaluminum oxy-compounds and/or ionizing ionic compounds, etc. In addition, as new olefin polymerization catalyst components there have been proposed metal amide compounds comprising titanium and diamine-based ligands, as represented by the following formulas (Macromolecules 1996, 29, 5241-5243; J. Am. Chem. Soc. 1996, 118. 10008-10009). ##STR2##
wherein R represents 2,6-(iso-Pr).sub.2 -C.sub.6 H.sub.3 -- or 2,6-Me.sub.2 -C.sub.6 H.sub.3 --, and R' represents --Me or --CH.sub.2 Ph.
These metal amide compounds are used in combination with aluminoxanes or B(C.sub.6 F.sub.5).sub.3, but their polymerization activity is inadequate.
Recently there have also been proposed new olefin polymerization catalysts, for example the olefin polymerization catalysts described in Japanese Laid-open Patent Publication No. 245713/96 comprising a titanium amide compound with a titanium-nitrogen bond and an aluminoxane.
Also, in Organometallics 1996, 15, 562-569 there are described organometallic complexes of Group 4 of the Periodic Table, having bis(borylamide) ligands represented by [Mes.sub.2 BNCH.sub.2 CH.sub.2 NBMes.sub.2 ].sup.-2, and it is stated that the complexes exhibit slight ethylene polymerization activity.
Incidentally, since olefin polymers generally have excellent mechanical properties, etc., they are used in various fields as different types of molds, but with the diversifying demands for properties of olefin polymers in recent years, olefin polymers with different characteristics have been desired. Improved productivity has also been a goal.
Because of these circumstances, there has been a demand for development of olefin polymerization catalysts with excellent olefin polymerization activity which can give olefin polymers with excellent properties, as well as a process for producing such olefin polymers.
In addition, organoaluminum oxy-compounds (aluminoxanes) used with transition metal compounds for polymerization of olefins are usually produced by contacting an organoaluminum compound such as trialkylaluminum with a metal salt hydrate in a hydrocarbon solvent. The hydrocarbon used here is an aromatic hydrocarbon, especially toluene, which has excellent ability to dissolve the resulting organoaluminum oxy-compound, and such organoaluminum oxy-compounds are usually sold as solutions in toluene, so that they are added to polymerization systems as solutions in toluene when they are used for polymerization. However, addition of an aromatic hydrocarbon such as toluene to a polymerization system raises the problem of residual odor in the polymer, and sometimes problems also arise with respect to working environment conditions. Although there have been methods for distilling toluene out from organoaluminum oxy-compounds for use of the organoaluminum oxy-compounds in solid form, these methods are not industrially convenient.
As a result of diligent research in light of the prior art, the present inventors have completed the present invention upon the finding that when (copolymerization of an olefin is carried out in the presence of a transition metal amide compound and an organoaluminum oxy-compound, addition of the organoaluminum oxy-compound to the polymerization system as an aliphatic or alicyclic hydrocarbon slurry can avoid causing the problems mentioned above and can give better polymerization activity than when the organoaluminum oxy-compound is added to the polymerization system as an aromatic hydrocarbon solution.